Spray systems, particularly pressurized spray systems, are well-known in the art. Such spray systems often utilize a metal can, plastic container or other package charged with a propellant. The propellant pressurizes the contents of the spray system to a pressure greater than atmospheric. Upon release of the propellant pressurizing the contents of the package, the pressure differential causes discharge of the contents to the atmosphere or ambient surroundings.
Typical propellants include compressed gasses, such as nitrogen, or hydrocarbon such as butane. One characteristic common to both compressed gas and hydrocarbon propellants is that the pressure decays with repeated uses, as illustrated. Such pressure decay may transmogrify the delivery characteristics of the contents of the package. However, the pressure decay of a compressed gas system is typically more noticeable throughout the life of the system. In contrast, hydrocarbon systems tend to regenerate, providing a generally more consistent pressure throughout much of the system life. Thus, only compressed gas systems are considered below.
Typical products contained in such packages include cleaners, furniture polish, perfumes, room deodorizers, spray paint, insecticides, lubricants, hair spray, medicine, etc. Each of these products has a desirable range of delivery characteristics, such as flow rate, cone angle and particle size. The flow rate is the amount of product delivered per unit time. The cone angle is the dispersion of the product over a particular area at a particular distance. The particle size is the distribution of average droplet size upon contacting the target surface or ambient at a predetermined distance from the nozzle orifice.
However, over time, the pressure decay of the propellant causes each of these delivery characteristics to change. The user may be able to compensate for some of these changes. For example, as the delivery rate decreases, the user may be able to simply dispense for a longer period of time. Likewise, as the cone angle decreases the consumer may be able to simply sweep the product over a larger area during dispensing or adjust the distance to the target surface.
However, as particle size increases during the pressure decay, the user is not able to compensate. An increase in particle size may be undesirable. For example, as particle size of a hairspray increases, the polymer may become too sticky. As particle size of a furniture polish increases, the polish may smear upon application. Particle size may also affect perfume release or suspension.
Accordingly, there is a need in the art to decouple couple particle size from the number of uses over the life of a product dispensed from a spray system. Some attempts have already been made in the art. For example EP 0,479,796 B1 issued to Pool et al. suggests that having a flow area ratio between the valve port and actuator outlet of at least 2:1 provides advantageous flow characteristics. However, some ratios less than 2:1 have been found to work well while some ratios greater than 2:1 have been found unsuitable. Accordingly, another approach is necessary.